|
|
Browse All
:
Moon of Hamilton and Jet Propulsion Laboratory (JPL)
|
Printer Friendly |
Many Worlds, Many Craters
| title |
Many Worlds, Many Craters |
| description |
A comparison of ~30-kilometer-diameter impact craters on several planetary bodies. All craters are shown at the same scale and have been rotated so that the light source is from the left. This rotation puts north at the bottom of the images of the lunar crater and the Ganymede crater. Names and locations of the four craters are as follows: Golubkhina (Venus), 60.30N, 286.40E, Kepler (Moon), 8.10N, 38.10W, (Mars), 20.80S, 53.60E, (Ganymede), 29.80S, 136.00W. *Image Credit*: Image of Ganymede Crater contributed by Paul Schenk (Lunar and Planetary Institute). Image of Mars crater obtained from the Mars Multi-Scale Map, Calvin Hamilton (Los Alamos National Laboratory). Images of lunar and venusian craters from Robert Herrick (Lunar and Planetary Institute). |
|
Heritage Project Celebrates
…
| Title |
Heritage Project Celebrates Five Years of Harvesting the Best Images from Hubble Space Telescope |
| General Information |
What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. Back to top [ #top ] |
|
Io Rotating
| Title |
Io Rotating |
| Explanation |
The surface of Io is continually changing. Jupiter's moon [ http://antwrp.gsfc.nasa.gov/apod/ap990920.html ] is the home to many powerful volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap991126.html ] so active they are effectively turning the moon inside out. The above time-lapse sequence [ http://solarviews.com/cap/jup/vio1.htm ] is a composite of images taken during two space missions that approached the violent moon: Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] and Galileo [ http://www.jpl.nasa.gov/galileo/mission.html ]. The sequence shows Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] during a complete rotation, which corresponds to a complete revolution around Jupiter [ http://www.jpl.nasa.gov/galileo/Jovian.html ] since Io [ http://cass.jsc.nasa.gov/pub/research/outerp/io.html ] always keeps the same face toward the giant planet. The rampant volcanism is thought to be caused by Jupiter's more distant Galilean Moons [ http://solarviews.com/eng/galdisc.htm ] (Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ], Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]) pulling on Io and continually distorting its shape, causing internal frictional [ http://www.cord.edu/dept/physics/p128/lecture99_12.html ] heating. Io is composed mostly of rock, with the yellow color originating from sulfur [ http://chemlab.pc.maricopa.edu/periodic/S.html ]. The causes of many of the other colors remain a topic of research [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999Icar..140..265G ]. |
|
Europa Rotating
| Title |
Europa Rotating |
| Explanation |
Evidence has been mounting that beneath the vast planes of ice that cover Europa [ http://antwrp.gsfc.nasa.gov/apod/ap961120.html ] lies water -- liquid oceans that might be home to alien life [ http://www.sciam.com/0497issue/0497scicit7.html ]. The smallest of Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s Galilean Moons [ http://solarviews.com/eng/galdisc.htm ] (which include Io [ http://www.seds.org/nineplanets/nineplanets/io.html ], Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]), Europa's deep interior is composed of mostly of silicate rock [ http://windows.arc.nasa.gov/cgi-bin/tour_def/glossary/silicate_rock.html ]. Upon close inspection, many surface cracks [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] stop abruptly only to continue on somewhere else -- indicating surface plates that might be sliding [ http://antwrp.gsfc.nasa.gov/apod/ap970410.html ]. The above time-lapse sequence [ http://www.solarviews.com/cap/jup/veuropa1.htm ] is a composite of images taken during the Voyager spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] flyby of the moon twenty years ago. Not all regions are resolved in high detail. The movie shows Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ] during a complete rotation, which corresponds to a complete revolution around Jupiter [ http://www.jpl.nasa.gov/galileo/Jovian.html ] since Europa [ http://cass.jsc.nasa.gov/pub/research/outerp/euro.html ] always keeps the same face toward the giant planet. The cause of many of the surface colors on Europa [ http://www.solarviews.com/eng/europa.htm ] also remains a topic of research [ http://antwrp.gsfc.nasa.gov/apod/ap010116.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988Icar...75..437B ]. |
|
Neptune: Big Blue Giant
| Title |
Neptune: Big Blue Giant |
| Explanation |
This picture was taken by the Voyager 2 [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] spacecraft in 1986 - the only spacecraft ever to visit Neptune. Neptune [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/neptune.html ] will be the farthest planet from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] until 1999, when the elliptical orbit of Pluto will cause it to once again resume this status. Neptune [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/neptune.html ], like Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ], is composed mostly of liquid water, methane and ammonia, is surrounded by a thick gas atmosphere of mostly hydrogen and helium, and has many moons and rings. Neptune [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-neptune.html ]'s moon Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] is unlike any other and has active volcanoes. The nature of Triton [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/triton.html ]'s unusual orbit around Neptune is the focus of much discussion and speculation. Tomorrow's picture: Pluto: The Frozen Planet |
|
Venus: Earth's Sister Planet
| Title |
Venus: Earth's Sister Planet |
| Explanation |
This picture in visible light was taken by the Galileo [ http://nssdc.gsfc.nasa.gov/planetary/galileo.html ] spacecraft. Venus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html ] is very similar to Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ] in size and mass - and so is sometimes referred to as Earth's sister planet - but Venus has a quite different climate. Venus' [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/venus.html ] thick clouds and closeness to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] (only Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap950814.html ] is closer) make it the hottest planet - much hotter than the Earth. Humans could not survive there, and no life of any sort has ever been found. When Venus [ http://nssdc.gsfc.nasa.gov/photo_gallery/PhotoGallery-Venus.html ] is visible it is usually the brightest object in the sky after the Sun and the Moon. More than 20 spacecraft have visited Venus including Venera 9, which landed on the surface, and Magellan [ http://stardust.jpl.nasa.gov/mveg/guide.html ], which used radar to peer through the clouds and make a map of the surface. There are still many things about Venus's unusual atmosphere that astronomers don't understand. Tomorrow's picture: Uranus: The Tilted Planet |
|
Ganymede: Moonquake World
| Title |
Ganymede: Moonquake World |
| Explanation |
Ganymede [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ganymede.html ] probably undergoes frequent ground shaking events not unlike terrestrial earthquakes. Ganymede [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/ganymede.html ], the largest moon of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ] and the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ], has a thick outer coating of water ice. Passing Voyager spacecraft found a large number of cracks and grooves in the ice so it is thought that Ganymede, like the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ], has large shifting surface masses called tectonic plates. Ganymede was discovered by Galileo [ http://galileo.imss.firenze.it/museo/4/index.html ] and Marius [ http://seds.lpl.arizona.edu/billa/tnp/help.html#M ] in 1610, and is larger than the planets Mercury and Pluto. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter is December of 1995. Tomorrow's picture: Europa: Ancient Water World |
|
Europa: Ancient Water World
| Title |
Europa: Ancient Water World |
| Explanation |
Beneath the cold icy surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s moon Europa [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html ] are probably the only oceans of water in our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] outside of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]. These oceans, possibly 50 kilometers deep, might also be the most likely local place to find extra-terrestrial life. Europa [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/europa.html ]'s smooth surface is unlike any other known planet or moon, giving evidence for relatively few craters or mountains. Europa was discovered by Galileo [ http://galileo.imss.firenze.it/museo/4/index.html ] and Marius [ http://seds.lpl.arizona.edu/billa/tnp/help.html#M ] in 1610. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter in December of 1995. Tomorrow's picture: Callisto: Dark Smashed Iceball |
|
Saturn's Moon Dione
| Title |
Saturn's Moon Dione |
| Explanation |
Dione [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/dione.html ], one of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ]'s larger moons, is remarkable for its bright surface streaks. These streaks run across some of Dione's many craters, which indicate that the process which created the streaks occurred later than the process which created the craters. Dione [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/dione.html ] is made of mostly water ice but its relatively high density indicates that it contains much rock inside. Dione was discovered by Giovanni Cassini in 1684. NASA's Cassini mission [ http://newproducts.jpl.nasa.gov/calendar/cassini.html ] to Saturn is currently scheduled for launch in October 1997. Dione's orbit is remarkable it that it also houses the much smaller moon Helene [ http://antwrp.gsfc.nasa.gov/apod/ap951010.html ]. This moon, once designated "Dione B", precedes Dione by about 1/6th of an orbit. |
|
Jupiter's Moon Amalthea
| Title |
Jupiter's Moon Amalthea |
| Explanation |
Amalthea is Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s fifth largest moon, much smaller than the four Galilean [ http://bang.lanl.gov/video/stv/arshtml/arstoc.html ] satellites Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ]. The orbit of Amalthea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/amalthea.html#amalthea ] is inside of these moons, and with its long axis always pointing toward Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]. It's dark surface color is probably due to sulfur being expelled from Io [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ]. Amalthea is not massive enough for its internal gravity to make it spherical. Amalthea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/amalthea.html ] was discovered in 1892 by Edward Barnard. |
|
Iapetus: Saturn's Disappeari
…
| Title |
Iapetus: Saturn's Disappearing Moon |
| Explanation |
Iapetus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/iapetus.html ] has an unusual surface, one half of which is very dark, the other half very light. This caused it's discoverer Cassini [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/help.html#cassini ] to remark that Iapetus [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/iapetus.html ] could only be seen when on one side of Saturn but not the other. The reason for the difference between hemispheres is presently unknown. Iapetus is the third largest of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ]'s moon behind Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.html ] and Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap951014.html ]. Iapetus is composed predominantly of water ice. |
|
Rhea: Saturn's Second Larges
…
| Title |
Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/rhea.html ] is the second largest moon of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ], behind Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/rhea.html ]'s rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph was taken with the Voyager 1 spacecraft in 1980. |
|
Saturn's Moon Tethys
| Title |
Saturn's Moon Tethys |
| Explanation |
Tethys is one of the larger and closer moons of Saturn. It was visited by both Voyager spacecraft [ http://voyager.jpl.nasa.gov/ ] - Voyager 1 in November 1980 and by Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ] 2 in August 1981. Tethys [ http://www.nineplanets.org/tethys.html ] is now known to be composed almost completely of water ice. Tethys [ http://www.solarviews.com/eng/tethys.htm ] shows a large impact crater [ http://antwrp.gsfc.nasa.gov/apod/ap990711.html ] that nearly circles the planet. That the impact that caused this crater did not disrupt the moon is taken as evidence that Tethys [ http://sse.jpl.nasa.gov/features/planets/saturn/tethys.html ] was not completely frozen in its past. Two smaller moons, Telesto [ http://www.nineplanets.org/tethys.html#telesto ] and Calypso [ http://www.nineplanets.org/tethys.html#calypso ], orbit Saturn [ http://antwrp.gsfc.nasa.gov/apod/saturn.html ] just ahead of and behind Tethys. Giovanni Cassini [ http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Cassini.html ] discovered Tethys in 1684. In 1997, NASA [ http://www.nasa.gov/ ] launched [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] a spacecraft named Cassini [ http://saturn.jpl.nasa.gov/cassini/english/spacecraft/ ] to Saturn that will arrive in 2004. |
|
Saturn's Moon Tethys
| Title |
Saturn's Moon Tethys |
| Explanation |
Tethys [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/tethys.html ] is one of the larger and closer moons of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap951018.html ]. It was visited by both Voyager spacecraft - Voyager 1 in November 1980 and by Voyager 2 in August 1981. Tethys [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/tethys.html ] is now known to be composed almost completely of water ice. Tethys shows a large impact crater that nearly circles the planet. That the impact that caused this crater did not disrupt the moon is taken as evidence that Tethys was not completely frozen in its past. Tethys has two moons named Telesto [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/tethys.html#telesto ] and Calypso [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/tethys.html#calypso ] that orbit just ahead of it and behind it. Tethys was originally discovered in 1684 by Giovanni Cassini. |
|
Uranus' Moon Ariel: Valley W
…
| Title |
Uranus' Moon Ariel: Valley World |
| Explanation |
What formed Ariel [ http://bang.lanl.gov/solarsys/ariel.htm ]'s valleys? This question presented itself when Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed this satellite of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Speculation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990Icar%2E%2E%2E87%2E%2E110T&db_key=AST ] includes that heating caused by the ancient tides of Uranus caused moonquakes and massive shifting of the moon's surface. In any event, a huge network of sunken valleys was found to cover this frozen moon, and some unknown material now coats the bottoms of many of these channels. Ariel [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ariel.html ] is the second closest to Uranus outside of Miranda [ http://antwrp.gsfc.nasa.gov/apod/ap951224.html ], and is composed of roughly half water ice and half rock. Ariel was discovered by William Lassell [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/help.html#lassell ] in 1851. |
|
Uranus's Moon Oberon: Impact
…
| Title |
Uranus's Moon Oberon: Impact World |
| Explanation |
Oberon is the most distant and second largest moon of Uranus. Discovered by William Herschel [ http://www.adventure.com/library/encyclopedia/space/herschls.html ] in 1787, the properties of the world remained relatively unknown until the robot spacecraft Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed it during its flyby of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Compared to Uranus' moons Ariel [ http://antwrp.gsfc.nasa.gov/apod/ap960303.html ], Titania [ http://antwrp.gsfc.nasa.gov/apod/ap960304.html ], and Miranda [ http://antwrp.gsfc.nasa.gov/apod/ap951224.html ], Oberon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/oberon.html ] is heavily cratered, and in this way resembles Umbriel [ http://antwrp.gsfc.nasa.gov/apod/ap960407.html ]. Like all of Uranus' large moons, Oberon [ http://bang.lanl.gov/solarsys/oberon.htm ] is composed of roughly half ice and half rock. Note that Oberon has at least one large mountain, visible on the limb at the lower left, that rises 6 km off the surface. |
|
Uranus's Moon Umbriel: A Mys
…
| Title |
Uranus's Moon Umbriel: A Mysterious Dark World |
| Explanation |
Why is Umbriel so dark? This dark moon reflects only half the light of other Uranus' [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] moons such as Ariel [ http://antwrp.gsfc.nasa.gov/apod/ap960303.html ]. And what is that bright ring at the top? Unfortunately, nobody yet knows. These questions presented themselves when Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed this satellite of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Voyager found an old surface with unusually large craters, and determined Umbriel [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/umbriel.html ]'s composition to be about half ice and half rock. Umbriel [ http://bang.lanl.gov/solarsys/umbriel.htm ] is the fourth largest and third most distant of Uranus' five large moons. Umbriel was discovered in 1851 by William Lassell [ http://www.ast.cam.ac.uk/~naw96/lassell/lassell.htm ]. |
|
Europa's Surface
| Title |
Europa's Surface |
| Explanation |
Voyager spacecraft [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-voyager.html ] images of Europa's surface [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html ], like the one above, are suggestive of sea ice on Earth [ http://antwrp.gsfc.nasa.gov/apod/ap951118.html ]. The criss-crossing dark streaks may indeed be cracks in its ice-covered surface caused by Jupiter's tidal stresses accompanied by the freezing and expansion of an underlying layer of water [ http://antwrp.gsfc.nasa.gov/apod/ap960806.html ]. This tantalizing prospect of oceans of liquid water [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ] beneath its frozen surface has helped make the smallest of the Galilean [ http://galileo.imss.firenze.it/museo/4/index.html ] moon's of Jupiter a planned focus of the Galileo spacecraft's ongoing mission to explore the Jovian system. New Europa images and results [ http://newproducts.jpl.nasa.gov/galileo/index.html ] from the Galileo mission were released today revealing [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1996/96-164.txt ] details which further suggest that Europa's icy surface was once - and may still be - supported on slush or liquid water. |
|
A Close-Up of the Lagoon Neb
…
| Title |
A Close-Up of the Lagoon Nebula |
| Explanation |
Ribbons of red-glowing gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] and dark dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] surround massive young stars in this close-up of the Lagoon Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap960127.html ] taken by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ]. The Lagoon Nebula [ http://seds.lpl.arizona.edu/billa/twn/n6523x.html ] is relatively close and bright - it appears larger than the Full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap960730.html ] and is visible even without a telescope [ http://aci.mta.ca/TheUmbrella/Physics/Astronomy/Telescope.html ]. Light takes about 5000 years to reach here from there. The Lagoon Nebula [ http://seds.lpl.arizona.edu/messier/m/m008.html ] houses the open star cluster [ http://antwrp.gsfc.nasa.gov/apod/lib/open_clusters.html ] M [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#messier ]8. This photograph [ http://scivax.stsci.edu/~hamilton/nuggets/HST_NUGGETS.HTML ] is combination of exposures taken in the red, green and ultraviolet. The unusual bright central part of the Lagoon Nebula [ http://adsabs.harvard.edu/cgi-bin/nph-article_query?bibcode=1990ApJ%2E%2E%2E357%2E%2E502M&page=1&plate_select=NO&type=GIF ] (lower left in this image) is known as the Hourglass Nebula. |
|
Rhea: Saturn's Second Larges
…
| Title |
Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://www.nineplanets.org/rhea.html ] is the second largest moon of Saturn [ http://pds.jpl.nasa.gov/planets/choices/saturn1.htm ], behind Titan [ http://www.nineplanets.org/titan.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.solarviews.com/eng/rhea.htm ]'s rotation and orbit are locked together (just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ]) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph [ http://www.solarviews.com/cap/sat/rhea2.htm ] was taken with the Voyager 1 spacecraft [ http://voyager.jpl.nasa.gov/spacecraft/index.html ] in 1980. NASA's Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ] is currently on route to Saturn and will arrive in 2004. |
|
Venus: Earth's Cloudy Twin C
…
| Title |
Venus: Earth's Cloudy Twin Credit: Galileo [ http://galileo.jpl.nasa.gov/ ] Spacecraft, JPL [ http://www.jpl.nasa.gov/ ], NASA [ http://www.nasa.gov/ ]; |
| Explanation |
This picture by the Galileo spacecraft [ http://nssdc.gsfc.nasa.gov/planetary/galileo.html ] shows just how cloudy Venus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html ] is. Venus [ http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34067 ] is very similar to Earth [ http://antwrp.gsfc.nasa.gov/apod/ap010204.html ] in size and mass - and so is sometimes referred to as Earth's sister planet - but Venus [ http://pds.jpl.nasa.gov/planets/welcome/venus.htm ] has a quite different climate. Venus [ http://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Pioneer.Venus/Venus.Discoveries ]' thick clouds and closeness to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap980830.html ] (only Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap010819.html ] is closer) make it the hottest planet - much hotter than the Earth [ http://antwrp.gsfc.nasa.gov/apod/earth.html ]. Humans could not survive there, and no life of any sort has ever been found. When Venus is visible [ http://www.space.com/spacewatch/venus_guide_031024.html ] it is usually the brightest object in the sky after the Sun and the Moon [ http://antwrp.gsfc.nasa.gov/apod/moon.html ]. More than 20 spacecraft have visited Venus [ http://nssdc.gsfc.nasa.gov/photo_gallery/PhotoGallery-Venus.html ] including Venera 9 [ http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1975-050D ], which landed on the surface, and Magellan [ http://www.jpl.nasa.gov/magellan/ ], which used radar to peer through the clouds and make a map of the surface [ http://antwrp.gsfc.nasa.gov/apod/ap030427.html ]. This visible light picture of Venus [ http://antwrp.gsfc.nasa.gov/apod/venus.html ] was taken by the Galileo spacecraft [ http://antwrp.gsfc.nasa.gov/apod/ap951206.html ] that orbited Jupiter from 1995 to 2003. Many things about Venus remain unknown, including the cause of mysterious bursts of radio waves [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995JATP...57..557S ]. |
|
Rhea: Saturn's Second Larges
…
| Title |
Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://www.seds.org/nineplanets/nineplanets/rhea.html ] is the second largest moon of Saturn [ http://pds.jpl.nasa.gov/planets/welcome/saturn.htm ], behind Titan [ http://www.seds.org/nineplanets/nineplanets/titan.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.solarviews.com/eng/rhea.htm ]'s rotation and orbit are locked together (just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ]) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea [ http://cass.jsc.nasa.gov/pub/research/outerp/rhea.html ]'s leading surface is much more heavily cratered than its trailing surface. The above photograph [ http://www.solarviews.com/cap/sat/rhea2.htm ] was taken with the Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ] 1 spacecraft in 1980. |
|
|
![Venus: Earth's Cloudy Twin Credit: Galileo [ http://galileo.jpl.nasa.gov/ ] Spacecraft, JPL [ http://www.jpl.nasa.gov/ ], NASA [ http://www.nasa.gov/ ];](http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size1/NVA2-4-NA/6350/venus2_gal_big.jpg&userid=1&username=admin&resolution=1&servertype=JVA&cid=4&iid=NVA2&vcid=NA&usergroup=NASA_Astronomy_Picture_of_the_Day_Collecti-4-Admin&profileid=16)
